As the SHGC falls in single-pane tinted glazings, the daylight
transmission (VT) drops even faster, and there are practical limits on
how low the SHGC can be made using tints. If larger reductions are desired,
a reflective coating can be used to lower the solar heat gain coefficient
by increasing the surface reflectivity of the material. These coatings
usually consist of thin metallic or metal oxide layers. The reflective
coatings come in various metallic colors-silver, gold, bronze-and they
can be applied to clear or tinted glazing. The solar heat gain coefficient
can be reduced by varying degrees, depending on the thickness and reflectivity
of the coating, and its location in the glazing system. Some reflective
coatings are durable and can be applied to exposed surfaces; others must
be protected in sealed insulating glass units.
Figure 3-17 illustrates a highly reflective coating placed over a bronze-tinted,
double-glazed unit. The emittance of the coating creates modest changes
in the U-factor.
As with tinted glazing, the visible transmittance of a reflective glazing
usually declines more than the solar heat gain coefficient. Reflective
glazings are usually used in commercial buildings for large windows, for
hot climates, or for windows with substantial solar heat gains. Reflective
glazing is also used by many architects because of its glare control and
uniform, exterior appearance.
The reflective coating is applied just like hardcoat Low-E through spraying
(Pyrolitic process) during the float glass manufacturing process.
Reflects light and heat with a metal oxide coating giving a mirror effect.
Minimizes solar heat gain, and ultraviolet light damage to interior.
Adds daytime privacy.
May be tempered.
Note: Heat absorbing and heat reflective glass can only be used on the
exterior lite of a unit in order to avoid a build-up of heat inside the
airspace, which will cause thermal stress cracks or seal failure.
Note: Reflective type glass works with the play of light. Example: During
daylight hours you can't see inside a building with reflective glass,
(only your refection). At night there is just the opposite effect. You
can see in, but the people inside can not see out.